There is no need to drill the bottom of a FG dinghy. The standard transducer for a simple dinghy installation is a "transom mount" TD. That TD will epoxy to the Fg in the bottom of the hull and will give you good readings to 1000 ft. That is how I have fastened my TD, wihich I did in 2010. It is simple to do and will last the life of your ownership of the dinghy.

Since my dinghy has no electrical system we lay a simple 6ft length of PVC pipe marked at 4ft down along the centerline just in case. The long end is for the Monk, the short for the dinghy. Have not needed it yet.